1. Field of the Invention
This invention relates to the synthesis and in vivo application of compounds which have antibiotic activity against microbes that synthesize mycolic acid, including Mycobacterium sp., particularly drug resistant Mycobacierium strains, and to the use of these compounds to treat any susceptible pathogenic microorganism or parasite.
2. Review of Related Art
The emergence of multiply drug resistant (MDR) strains of Mycobacterium tuberculosis and other atypical mycobacteria which infect immunocompromised patients (e.g., AIDS patients) highlights the need for continued antibiotic development.
Mycobacterium sp. synthesize a multitude of complex lipids and glycolipids unique to this genus, making these biochemical pathways attractive targets for drug therapy (Bloch, K., xe2x80x9cControl mechanisms for fatty acid synthesis in Mycobacterium smegmatis,xe2x80x9d Adv. Enzymol. 45:1-84, 1977; Brennan, P. J., and Nikaido, H., xe2x80x9cThe envelope of mycobacteria,xe2x80x9d Ann. Rev. Biochem. 64:29-63, 1995). The xcex2-ketoacyl synthase (KS) of particulate Type II fatty acid synthases or the corresonding domain of the polyfunctional Type I fatty acid synthases catalyzes the critical two-carbon homologation during buildup of the growing fatty acid chain. This process typically gives acids of length C16 to C18. In chain elongation of normal fatty acids, carried out for example by mycobacteria, CoA and/or acyl-carrier protein (ACP) thioesters of these acids are further reacted with malonyl-CoA to greatly extend their length to 60-90 carbons. These high molecular weight acids are known collectively as mycolic acids.
Mycolic acids are a group of complex, long, branched chain fatty acids that are vital for the growth and survival of mycobacteria. Mycolic acids comprise the single largest component of the mycobacterial cell envelope. Little is known about the nature of the biosynthetic enzymes involved, but evidence suggests some similarity to conventional fatty acid synthases (Bloch, 1977; Brennan, et al., 1995). These unusually long lipid molecules form a waxy coat of limited permeability.
The presence in mycobacteria of particular modified fatty acids having complex and well-organized structures presents a potentially attractive target for drug design (Young, D. B., and Duncan, K., xe2x80x9cProspects for new interventions in the treatment and prevention of mycobacterial disease,xe2x80x9d Ann Rev. Microbiol. 49:641-673, 1995). It has been suggested that isoniazid inhibits mycolic acid synthesis as its potential mechanism of action (Takayama, K., Wang, L., and David, H. L., xe2x80x9cEffect of isoniazid on the in vivo mycolic acid synthesis, cell growth, and viability of Mycobacterium tuberculosis,xe2x80x9d Antimicrob. Agents Chemother., 2:29-35, 1972; Takayarna, K., Schnoes, H. K., Armstrong, E. I., and Booyle, R. W., xe2x80x9cSite of inhibitory action of isoniazid in the synthesis of mycolic acids in Mycobacterium tuberculosis,xe2x80x9d J. Lipid Res., 16:308-317, 1975; Quemard A., Dessen A., Sugantino M., Jacobs W. R., Sacchettini J. C., Blanchard J. S. xe2x80x9cBinding of catalase peroxide-activated isoniazid to wild-type and mutant Mycobacterium tuberculosis enoyl-ACP reductases,xe2x80x9d J. Am. Chem. Soc., 118:1561-1562, 1996; Baldock C., Rafferty J. B., Sedenikova S. E., Baker P. J., Stuitje A. R., Slabas A. R., Hawkes T. R., Rice D. W. xe2x80x9cA mechanism of drug action revealed by structural studies of enoyl reductase,xe2x80x9d Science, 274:2107-2110, 1996; Quemard A., Sacchettini J. C., Dessen A., Vilcheze C., Bittman R., Jacobs W. R., Blanchard J. S., xe2x80x9cEnzymatic characterization of the target for isoniazid in Mycobacterium tuberculosis, Biochemistry, 34:8235-8241, 1993; Msluli, K., D. R. Sherman, M. J. Hickey, B. N. Kreiswirth, S. Morris, C. K. Stover, and C. E. Barry, III, xe2x80x9cBiochemical and genetic data suggest that InhA is not the primary target for activated isoniazid in Mycobacterium tuberculosis,xe2x80x9d J. Infect. Dis., 174:1085-1090, 1996; Dessen A., A. Quemard, J. S. Blanchard, W. R. Jacobs, and J. C. Saccettini, xe2x80x9cCrystal structure and function of the isoniazid target of Mycobacterium tuberculosis,xe2x80x9d Science, 267:1638-1641, 1995; Banejee, A., E. Dubnau, A. Quemard, V. Balasubramanian, K. S. Um, T. Wilson, D. Collins, G. deLisle, W. R. Jacobs, Jr., xe2x80x9cInhA, a gene encoding a target for isoniazid and ethionamide in Mycobacterium tuberculosis.xe2x80x9d Science, 263:227-230, 1994). This finding might be expected to stimulate a search for novel compounds that act upon the lipid synthetic pathways of mycobacteria as a fresh approach for antibiotic development. Surprisingly, however, lipid biosynthesis has not been exploited for drug development in these organisms. No drugs which specifically inhibit mycobacterial lipid synthesis have been developed other than isoniazid, and there remains a need for new drugs to treat the growing problem of multi-drug resistant mycobacteria.
This invention is directed to novel compounds having antimicrobial activity, particularly antimicrobial effectiveness against multi-drug resistant mycobacteria.
This invention is also directed to a method for treating mycobacterial infection by drug resistant strains through use of independent therapeutic targets.
These and other objects of the invention are achieved by one or more of the following embodiments. In one embodiment, this invention provides a compound having the formula: Rxe2x80x94SOnxe2x80x94Zxe2x80x94COxe2x80x94Y, where R is preferably an alkyl group having 6-20 carbons; Z is preferably a radical selected from xe2x80x94CH2xe2x80x94, xe2x80x94Oxe2x80x94, and xe2x80x94NHxe2x80x94, two of these radicals coupled together or xe2x80x94CH2xe2x95x90CH2xe2x80x94; Y is preferably xe2x80x94NH,2xe2x80x94Oxe2x80x94CHxe2x80x94CH65 xe2x80x94COxe2x80x94COxe2x80x94Oxe2x80x94CH3, or xe2x80x94Oxe2x80x94CH3; and n is 1 or 2. In particularly preferred embodiments, R is a branched alkyl group, or R is a linear alkyl group interrupted by an aromatic ring.
In another embodiment, this invention provides a method of inhibiting growth of a microbial cell which synthesizes xcex1-substituted, xcex2-hydroxy fatty acids. The method comprising treating the cell with a compound having the formula: Rxe2x80x94SOnxe2x80x94Zxe2x80x94COxe2x80x94Y, as described above. In particular, cells inhibited by the compound of this invention are cells which synthesize xcex1-substituted, xcex2-hydroxy fatty acids selected from the group consisting of corynemycolic acid, nocardic acid, and mycolic acid. Preferably, the method is used to inhibit growth of microbial cells selected from the group consisting of corynebacteria, nocardiae, rhodococcus, and mycobacteria. More preferably, the method is used to inhibit growth of mycobacterial cells, such as Mycobacterium tuberculosis, drug-resistant M. tuberculosis, M. avium intracellulare, M. leprae, or M. paratuberculosis. 
In yet another embodiment, this invention provides a method for treating a mycobacterial infection by administering to an animal a pharmaceutical composition containing a compound having the formula: Rxe2x80x94SOnxe2x80x94Zxe2x80x94COxe2x80x94Y, as described above.
The present inventors have synthesized and tested a number of sulfones and sulfoxides having structures based upon the reaction intermediates of the xcex2-ketoacyl synthase reaction of fatty acid synthase. A number of these compounds have demonstrated in vitro activity against virulent M. tuberculosis (see Table 1). The desireable characteristics found among the compounds tested included: potency, in vivo activity, reproducibility of MIC data, ease of synthesis, and chemical stability. Use of the compounds of this invention in drug therapy against multiply drug resistant tuberculosis will provide a means to treat both patients presently suffering from active disease, and the millions of potential patients who harbor quiescent disease which may become active as a result of immunosuppression or other systemic disease.